title: Fluctuations in phenylalanine concentrations in phenylketonuria: a review of possible relationships with outcomes.
abstract: Fluctuations in blood phenylalanine concentrations may be an important determinant of intellectual outcome in patients with early and continuously treated phenylketonuria (PKU). This review evaluates the studies on phenylalanine fluctuations, factors affecting fluctuations, and if stabilizing phenylalanine concentrations affects outcomes, particularly neurocognitive outcome. Electronic literature searches of Embase and PubMed were performed for English-language publications, and the bibliographies of identified publications were also searched. In patients with PKU, phenylalanine concentrations are highest in the morning. Factors that can affect phenylalanine fluctuations include age, diet, timing and dosing of protein substitute and energy intake, dietary adherence, phenylalanine hydroxylase genotype, changes in dietary phenylalanine intake and protein metabolism, illness, and growth rate. Even distribution of phenylalanine-free protein substitute intake throughout 24h may reduce blood phenylalanine fluctuations. Patients responsive to and treated with 6R-tetrahydrobiopterin seem to have less fluctuation in their blood phenylalanine concentrations than controls. An increase in blood phenylalanine concentration may result in increased brain and cerebrospinal fluid phenylalanine concentrations within hours. Although some evidence suggests that stabilization of blood phenylalanine concentrations may have benefits in patients with PKU, more studies are needed to distinguish the effects of blood phenylalanine fluctuations from those of poor metabolic control.
authors.affiliation: Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK. Electronic address: Maureen.Cleary@gosh.nhs.uk.
authors.forename: Maureen
authors.initials: M
authors.lastname: Cleary
authors.forename: Friedrich
authors.initials: F
authors.lastname: Trefz
authors.forename: Ania C
authors.initials: AC
authors.lastname: Muntau
authors.forename: François
authors.initials: F
authors.lastname: Feillet
authors.forename: Francjan J
authors.initials: FJ
authors.lastname: van Spronsen
authors.forename: Alberto
authors.initials: A
authors.lastname: Burlina
authors.forename: Amaya
authors.initials: A
authors.lastname: Bélanger-Quintana
authors.forename: Maria
authors.initials: M
authors.lastname: Giżewska
authors.forename: Christoph
authors.initials: C
authors.lastname: Gasteyger
authors.forename: Esther
authors.initials: E
authors.lastname: Bettiol
authors.forename: Nenad
authors.initials: N
authors.lastname: Blau
authors.forename: Anita
authors.initials: A
authors.lastname: MacDonald
mesh_terms: D000328:Adult; D000367:Age Factors; D001708:Biopterins / Q000031:analogs & derivatives* / Q000627:therapeutic use; D004032:Diet; D006801:Humans; D010649:Phenylalanine / Q000097:blood* / Q000235:genetics* / Q000378:metabolism; D010651:Phenylalanine Hydroxylase / Q000235:genetics / Q000378:metabolism; D010661:Phenylketonurias / Q000097:blood* / Q000188:drug therapy / Q000235:genetics / Q000503:physiopathology; D039781:PubMed
chemical_list: D001708:Biopterins; D010649:Phenylalanine; D010651:Phenylalanine Hydroxylase; C003402:sapropterin
keywords: 6R-tetrahydrobiopterin; BH(4); ECT; HPA; Hyperphenylalaninemia; IDC; IQ; LNAA; PAH; PKU; Phenylalanine fluctuations; Phenylketonuria; SD; SEE; Sapropterin; Tyr; WISC; Wechsler Intelligence Scale for Children; early and continuously treated; hyperphenylalaninemia; index of dietary control; intelligence quotient; large neutral amino acid; phenylalanine hydroxylase; phenylketonuria; standard deviation; standard error of the estimate; tyrosine